Theatre Design & Technology - Oct 1966 - 17

MAX DROP is
load.
the
voltage
drop at full output and full
MIN LOAD is the smallest load for satisfactory operation
LOAD REG is change In output voltage as the load varies
from full load to 1 6 of full load.
LINE REG IS ratiO of the change in output voltage ior a
change in input voltage. The value at the light
of the vertical bar gives the output voltage level
for which the specification was written or test
conducted.
CURVE
is
the
specified
control
curve
of
the dimmer.
ACOUSTIC NOISE (lamp) is the noise output at a lamp
filament caused by the rapid turn-on of the SCR.
I
2
3
4
6
MAX DROP
S'-'
SV
7V
3V
5V
MIN LOAD
S5W
75W
600W
40W
100W
I.SV
3.6V
LINE REG
us I60
1.~5160
CURVE ±5%
10-6
ACOUSTIC
NOISE (LAMPl
YES
LOAD REG
l
Fig. 4:
6V
1.4 V
1.4 V
16 160
4~160
5-212
10-3
10-2
6-3
YES
YES
YES
YES
1
40
160
A more serious load-related problem is the poor performance of all dimmers at small loads. It would seem desirable for any dimmer to be connected to any load
within its rating without resorting to special "ghost"
loading.
If this property is missing, the load and the dimmer must
be fitted together. Such rearrangements lead to extensive
and time consuming alterations of the bank configuration,
and the necessity of maintaining an elaborate bookkeeping
system. All of the dimmers in this test series exhibited
sharp overshoots, and often continued high frequency ringing when the dimmer was driving a small load. This
overshoot and the remainder of the transient contain very
high frequency energy which is a serious interference
hazard to audio radio and video service nearby.
Any unbalanced loading of the three phase input feed will
cause the line voltage to a dimmer to vary. In addition
the normal pattern of power demand by the community
will result in changes in line level. These line voltage
changes will cause unscheduled alteration of the lighting
design unless the dimmer circuitry provides an output
voltage which is constant over the normal range of line
variations.
Tabular Results for Five Designs Tested
Figure 4 displays the results of our tests. The designation curve ±. 5 % refers to the part of the range of the
manual controller (scale of 0-10 which stayed within +
5% of the specified curve.
The MIN LOAD measurement is that value of load which
produced an output voltage having a leading edge containing an overshoot transient of less than 5% of instantaneous voltage.
Some dimmer designs also exhibited instability in trigyering with very small loads (less than 100 watts) and one
unit became so unstable it would turn on to full voltage
and then not respond to manual control.
It could be said that in the areas of control curve, lamp
noise and internal losses, most manufacturers had a
somewhat optimistic idea of their unit's performance.
65
W
64
2
~
~
--l
o
>
63
t; 62
5
0...
f-
4
6
:::)
o
61
3
60
Another way of evaluating the test results is to look at
the comparative and absolute performance of the five
dimmer designs.
The load regulation of the dimmers was tested at 50V
rms with a maximum load of 5 KW. The load was then
reduced in steps to 2 KW while the output voltage was
monitored. The results of this routine are plotted in
Figure 5.
The ideal performance would be to have no change over
the full range of loading. Since most setting of light
levels by the lighting designer is done by eye and the
circuit loading of each dimmer is constant except when
some catastrophic failure occurs, it is questionable whether
good load regulation is required. The necessary readjustments made by the lighting operator to maintain adequate
visability are so much larger in scope than those caused
by any changes in the dimmer that it does not seem that
load regulation is an important attribute of an effective
lighting system.
OCTOBER 1966
2KW
3KW
4KW
6KW
LOAD
Fig. 5:
Load Regulation 'of 60V
In this test series, Iine regulation measurements were
made at the 50 volt, the 90 volt and the full voltage
output levels. The output level was monitored as the input to the dimmer was varied through a range of -15
volts to + 5 volts from nominal line voltage.
The results are
level, three of
regulation while
regulation. The
shown in Figure 5. At the sixty volt
the designs responded with nearly ideal
the other two units showed little or no
sixty volt level is the output at which
17